1. Field of the Invention
This invention relates to magnetic bubble domain systems, in general, and to relatively high yield, large capacity bubble domain memories, in particular.
2. Description of Prior Art
With the introduction of magnetic bubble domain devices, many devices have been developed. As these devices have been refined and improved, the bubble domain concept has progressed beyond the curiosity stage and into the realm of commercial utilization. To improve the utilization prospects, more and better systems and systems applications are being investigated and established. Some of the systems applications include storage means such as memories.
In a mass bubble memory system, such as a bubble memory recorder, it is frequently desirable to obtain maximum storage per individual chip in order to reduce the number of chips utilized. In particular, where data storage capacity is the prime consideration and access time is of secondary importance, it is desirable to increase the total capacity of the individual memory chip so that smaller numbers of chips are required. The utilization of smaller numbers of chips permits lower packaging and electronics costs as well as better system reliability. The capacity of an individual memory chip can be increased by interconnecting, in series, a large number of memory cells. Of course, such a serial arrangement produces a relatively slow access function. A faster access time can be obtained by using a major-minor loop configuration. Such a system is described in copending application, Ser. No. 689,312; entitled LARGE CAPACITY MAJOR-MINOR LOOP BUBBLE DOMAIN MEMORY WITH REDUNDANCY, by T. T. Chen; filed on May 24, 1976; assigned to the common assignee; and incorporated herein by reference.
Presently known chip design capabilities require that the basic memory unit is a single unit which is processed photolithographically. The size of this chip is limited by the basic size of the mask which can be properly handled by the photoreduction process. Therefore, to increase the capacity of the chip, it is necessary to increase the storage density of the mask which is limited by the resolution of the photolithographic technique.
At present, bubble domain technology permits processing of a large number of memory chips on a relatively large garnet wafer with reasonable yield. However, when an improved method and design of a storage cell is provided, a large number of interconnected cells can be placed on a wafer. The size of the composite chip is not, per se, limited by the photoreduction technique limitations.